Fluorine-containing polyether and lubricant comprising the same

ABSTRACT

A fluorine-containing polyether of the formula: 
     
         R.sub.f.sup.1 CF.sub.2 CF.sub.2 COOR.sub.f.sup.2           (I) 
    
     or 
     
         R.sub.f.sup.2 OCO--CF.sub.2 CF.sub.2 R&#39;.sub.f.sup.1 CF.sub.2 CF.sub.2 
    
      --COOR f   2                                         (II) 
     wherein R f   1  and R&#39; f   1  are each a group containing a perfluoroalkyl polyether group, and R f   2  is a fluorine-containing alkyl group or a fluorine-containing ether group, can be used as a lubricant which has good properties such as lubricity and durability properties.

This is a continuation-in-part application of Ser. No. 07/340,217 filedon Apr. 19, 1989, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a novel fluorine-containing polyetherand a lubricant comprising the same fluorine-containing polyether.

2. Description of the Related Art

A perfluoropolyether is a fluorine-containing oil which hasnon-flammability and good durability properties. However, theperfluoropolyether has a weak affinity to a surface of a material suchas a metal or glass. When it is thinly spread, for example, on a metalsurface and used as a lubricant, it has a problem such that durabilityis very poor because of migration. To solve this problem of theperfluoropolyether, a fluorine-containing polyether which has, at an endof the molecule, ##STR1## has been developed. However, thefluorine-containing polyether has defects in that those having thecarboxyl group must be carefully treated and that properties such aslubricity or durability are insufficient.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fluorine-containingpolyether which can be easily treated and has good properties such aslubricity and durability properties.

This and other objects are achieved by a fluorine-containing polyetherof the formula:

    R.sub.f.sup.1 CF.sub.2 CF.sub.2 COOR.sub.f.sup.2           (I)

or

    R.sub.f.sup.2 OCO--CF.sub.2 CF.sub.2 R'.sub.f.sup.1 CF.sub.2 CF.sub.2 --COOR.sub.f.sup.2                                        (II)

wherein R_(f) ¹ and R'_(f) ¹ are each a group containing aperfluoroalkyl polyether group, in which the perfluoroalkyl polyethergroup contains at least one repeating unit selected from the groupconsisting of a repeating unit of the formula:

    --C.sub.3 F.sub.6 O--                                      (a)

a repeating unit of the formula:

    --C.sub.2 F.sub.4 O--                                      (b)

and

a repeating unit of the formula:

--CF₂ O₁₃ (c)

provided that at least one of the repeating units (a) and (b) iscontained and the total number of the repeating units (a), (b) and (c)is at least three, and R_(f) ² is a fluorine-containing alkyl group or afluorine-containing ether group.

Also, the present invention provides a lubricant comprising saidfluorine-containing polyether.

BRIEF DESCRIPTION OF THE DRAWING

FIGURE is an IR chart of the fluorine-containing polyether of Example 1.

DETAILED DESCRIPTION OF THE INVENTION

In the perfluoroalkyl polyether group, the repeating unit: --C₃ F₆ O--includes --CF₂ CF₂ CF₂ O-- and --CF(CF₃)CF₂ O--. The repeating unit:--C₂ F₄ O-- is usually --CF₂ CF₂ O--.

The R_(f) ¹ group is, for example,

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.m --

wherein m is 3 to 200.

The R'_(f) ¹ group is, for example,

    --O(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.n (CF.sub.2).sub.6 (OCF.sub.2 CF.sub.2 CF.sub.2).sub.n O--

wherein each n is 2 to 200.

The R_(f) ² group is, for example,

C_(a) F_(2a+1) C_(b) H_(2b) -- (A)

wherein a is an integer of 1 to 10 and b is 1 or 2,

    H(C.sub.2 F.sub.4).sub.d CH.sub.2 --                       (B)

wherein d is an integer of 1 to 5,

or

    F(C.sub.3 F.sub.6 O).sub.1 (C.sub.2 F.sub.4 O).sub.m (CF.sub.2 O).sub.n CF.sub.2 CH.sub.2 --                                      (C)

wherein 1, m and n are each 0 or a positive integer provided that atleast one of 1 and m is not 0 and 1+m+n is not smaller than 3. In thefluorine-containing ether group (C), the order of each repeating unitmay not be the same as described above and is arbitrary in the molecule.

Specific examples of the fluorine-containing polyether according to thepresent invention are F(CF₂ CF₂ CF₂ O)_(m) CF₂ CF₂ COOCH₂ CF₂ CF₃ (1)

wherein m is 3 to 200, preferably 25 on the average,

    [HCF.sub.2 CF.sub.2 CH.sub.2 OCOCF.sub.2 CF.sub.2 O--(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.m --CF.sub.2 CF.sub.2 CF.sub.2 ].sub.2 -- (2)

wherein m is 2 to 200, preferably 20 on the average, and

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.m CF.sub.2 CF.sub.2 COOCH.sub.2 CF.sub.2 CF.sub.2 (OCF.sub.2 CF.sub.2 CF.sub.2).sub.n F   (3)

wherein m is 3 to 200, preferably 20 on the average and n is 2 to 200,preferably 20 on the average.

The fluorine-containing polyether according to the present invention canbe prepared by reacting a fluorine-containing compound of the formula:

    R.sub.f.sup.1 CF.sub.2 CF.sub.2 --COOH,

    R.sub.f.sup.1 CF.sub.2 CF.sub.2 --COF, or

    HOOC--CF.sub.2 CF.sub.2 R'.sub.f.sup.1 CF.sub.2 CF.sub.2 --COOH

wherein R_(f) ¹ and R'_(f) ¹ are the same as described above, with afluorine-containing alcohol of the formula:

    R.sub.f.sup.2 OH

wherein R_(f) ² is the same as described above. A catalyst such as anacid (e.g. sulfuric acid) is preferably used in the reaction. Thereaction is usually carried out at a temperature of 50° to 150° C. for 1to 10 hours.

The fluorine-containing polyether according to the present invention canbe used as a lubricant for materials such as a metal, glass, a silicagel and graphite. It is particularly useful as the lubricant for a thinfilm magnetic tape or a thin film magnetic disc.

A solution of the lubricant is preferably prepared by using a solvent soas to apply the lubricant on the surfaces of various materials. Specificexamples of the solvent are fluorine-containing solvents, for example,trichlorotrifluoroethane (e.g. Daiflon S-3 manufactured by DaikinIndustries, Ltd.), Cl(CF₂ CFCl)₂ Cl and N(C₃ F₇)₃. The solvent may beused in an amount of from 200 to 2000 parts by weight per part by weightof the lubricant.

The solution of the lubricant is then applied on a surface of asubstrate such a magnetic tape or a magnetic disc by dipping orspraying, and heated to form a lubricant film. The solvent is evaporatedby heating. The heating may be usually carried out at a temperature ofabout 80° C. The lubricant film may be formed to have a thickness of0.002 to 0.01 μm.

The reason as to why the lubricant according to the present inventionhas good properties such as lubricity and durability properties is notclearly known. It is assumed that since the metal, glass, silica gel andgraphite have many hydroxyl groups on their surfaces, thefluorine-containing polyether is adsorbed on their surfaces because of atransesterification occurring between the fluorine-containing polyetherand the hydroxyl group. When the fluorine-containing polyether has asufficiently higher acidity than that of the hydroxyl group on thesurface, the fluorine-containing alcohol moiety of thefluorine-containing polyether quickly transesterificates with thehydroxyl group on the surface. The transesterification is achieved inthe heating process to evaporate the solvent. The transesterification iscompleted by the frictional heat during use.

PREFERRED EMBODIMENTS OF THE INVENTION

The present invention is illustrated by the following Examples.

EXAMPLE 1

In a 200 ml three-neck flask, the fluorine-containing carboxylic acid:

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.p CF.sub.2 CF.sub.2 COOH

wherein p is 25 on the average (200 g, 57 mmol) and thenpentafluoropropanol (20 g, 130 mmol) were added and stirred. Then,concentrated sulfuric acid (0.5 ml) was added and the reaction wascarried out at 90° C. for 5 hours while stirring. The completion of thereaction was confirmed by disappearance of the absorption peak at 1780cm⁻¹ for the carboxylic acid and appearance of the absorption peak at1820 cm⁻¹ for the ester linkage in IR analysis. After the completion ofthe reaction, the reaction product was washed with water (100 ml) and alower phase was separated. Silica gel (30 g) was added to the lowerphase to remove the unreacted carboxylic acid. The reaction product wasfiltrated through a filter having a pore diameter of 0.2 iμm to obtainthe fluorine-containing polyether:

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.p CF.sub.2 CF.sub.2 COOCH.sub.2 CF.sub.2 CF.sub.3

wherein p is 25 on the average. Yield: 300 g (78%).

The IR chart of the resultant fluorine-containing polyether is shown inFIGURE.

EXAMPLE 2

To the fluorine-containing carboxylic acid:

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.q CF.sub.2 CF.sub.2 COOH

wherein q is 20 on the average (20 g), the fluorine-containing alcohol:

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.r CF.sub.2 CF.sub.2 CH.sub.2 OH

wherein r is 15 on the average (15 g) was added and stirred. Then,concentrated sulfuric acid (2 ml) was added and the reaction was carriedout at 150° C. for 10 hours while stirring. The completion of thereaction was confirmed by disappearance of the absorption peak at 1780cm⁻¹ for the carboxylic acid and appearance of the absorption peak at1820 cm⁻¹ for the ester linkage in IR analysis. After the completion ofthe reaction, the reaction product was washed with water (50 ml) threetimes and a lower phase was separated. Silica gel (100 g) was added tothe lower phase to remove the unreacted carboxylic acid. The reactionproduct was filtrated through a filter having a pore diameter of 0.2 μmto obtain the fluorine-containing polyether:

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.q CF.sub.2 CF.sub.2 COOCH.sub.2 CF.sub.2 CF.sub.2 (OCF.sub.2 CF.sub.2 CF.sub.2).sub.r F

wherein q is 20 and r is 15 on the average. Yield: 24 g (64%).

EXAMPLE 3

A two patch type hard disc having an uppermost carbon layer was dippedin a 0.1% by weight solution of the fluorine-containing polyether:

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.p CF.sub.2 CF.sub.2 COOCH.sub.2 CF.sub.2 CF.sub.3

wherein p is 25 on the average prepared in Example 1 intrichlorotrifluoroethane. The disc was removed from the solution andheated at 80° C. for one hour in an oven. A resultant lubricant film hada thickness of 0.01 μm.

The durability of the hard disc was tested by using a CSS Tester. After20,000 times, the μ value was not more than 0.5.

COMPARATIVE EXAMPLE

A hard disc was treated in the same manner as in Example 3 but using theperfluoropolyether oil:

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.p CF.sub.2 CF.sub.3

wherein p is 25 on the average instead of the fluorine-containingpolyether. A resultant lubricant film had a thickness of 0.01 μm. After1,100 times, the μ value exceeded 0.5.

What is claimed is:
 1. A fluorine-containing polyether of the formula:

    R.sub.f.sup.1 CF.sub.2 CF.sub.2 COOR.sub.f.sup.2           (I)

or

    R.sub.f.sup.2 OCO--CF.sub.2 CF.sub.2 R'.sub.f.sup.1 CF.sub.2 CF.sub.2 --COOR.sub.f.sup.2                                        (II)

wherein R_(f) ¹ and R'_(f) ¹ are each a group containing aperfluoroalkyl polyether group, in which the perfluoroalkyl polyethergroup contains at least one repeating unit selected from the groupconsisting of a repeating unit of the formula:

    --C.sub.3 F.sub.6 O--                                      (a)

a repeating unit of the formula:

    --C.sub.2 F.sub.4 O--                                      (b)

and a repeating unit of the formula:

    --CF.sub.2 O--                                             (c)

provided that at least one of the repeating units (a) and (b) iscontained and the total number of the repeating units (a), (b) and (c)is at least three, and R_(f) ² is a fluorine-containing alkyl group or afluorine-containing ether group.
 2. The fluorine-containing polyetheraccording to claim 1, wherein the R_(f) ² group is

    C.sub.a F.sub.2a+1 C.sub.b H.sub.2b --                     (A)

wherein a is an integer of 1 to 10 and b is 1 or 2,

    H(C.sub.2 F.sub.4).sub.d CH.sub.2 --                       (B)

wherein d is an integer of 1 to 5, or

    F(C.sub.3 F.sub.6 O).sub.1 (C.sub.2 F.sub.4 O).sub.m (CF.sub.2 O).sub.n CF.sub.2 CH.sub.2 --                                      (C)

wherein 1, m and n are each 0 or a positive integer provided that atleast one of 1 and m is not 0 and 1+m+n is not smaller than three. 3.The fluorine-containing polyether according to claim 1, wherein theR_(f) ¹ group is

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.p --

wherein p is an integer of 3 to 200, and the R_(f) ² group is --CH₂ CF₂CF₃.
 4. The fluorine-containing polyether according to claim 1, whereinthe R_(f) ¹ group is

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.q --

wherein q is an integer of 3 to 200, and the R_(f) ² group is

    --CH.sub.2 CF.sub.2 CF.sub.2 (OCF.sub.2 CF.sub.2 CF.sub.2).sub.r F

wherein r is an integer of 2 to
 200. 5. A lubricant comprising thefluorine-containing polyether according to claim
 1. 6. Afluorine-containing polyether of the formula:

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.m CF.sub.2 CF.sub.2 COOCH.sub.2 CF.sub.2 CF.sub.3                                         ( 1)

wherein m is 3 to 200,

    [HCF.sub.2 CF.sub.2 CH.sub.2 OCOCF.sub.2 CF.sub.2 O--(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.m --CF.sub.2 CF.sub.2 CF.sub.2 ].sub.2 -- (2)

wherein m is 2 to 200 or

    F(CF.sub.2 CF.sub.2 CF.sub.2 O).sub.m CF.sub.2 CF.sub.2 COOCH.sub.2 CF.sub.2 CF.sub.2 (OCF.sub.2 CF.sub.2 CF.sub.2).sub.n F   (3)

wherein m is 3 to 200 and n is 2 to 200.